1. Field of the Invention
This invention relates to a process for converting certain precursors to a high yield of para dialkyl substituted benzenes, such as para-xylene, utilizing a specified crystalline aluminosilicate zeolite catalyst.
2. Description of the Prior Art
The disproportionation of aromatic hydrocarbons in the presence of zeolite catalysts has been described by Grandio et al. in the Oil and Gas Journal, Vol. 69, No. 48 (1971). U.S. Pat. Nos. 3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961 show vapor-phase disproportionation of toluene over various catalysts.
In these prior art processes, the xylene product produced has the equilibrium composition of approximately 24 percent para, 54 percent meta and 22 percent ortho.
While the above-noted prior art is considered of interest in connection with the subject matter of the present invention, the conversion process described herein, utilizing a catalyst of particularly defined sorption properties comprising a crystalline aluminosilicate zeolite characterized by a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12, has not, insofar as is known, been heretofore described.
Of the xylene isomers, i.e., ortho, meta and para-xylene, meta-xylene is the least desired product, with ortho and para-xylene being the more desired products. Para-xylene is of particular value being useful in the manufacture of terephthalic acid which is an intermediate in the manufacture of synthetic fibers, such as "Dacron". Mixtures of xylene isomers, either alone or in further admixture with ethylbenzene, generally containing a concentration of about 24 weight percent para-xylene in the equilibrium mixture, have previously been separated by expensive superfractionation and multistage refrigeration steps. Such process, as will be realized, has involved high operation costs and has a limited yield.